1. Field of the Invention
The present invention relates to an arrangement for detecting a light emitting state or the brightness of a plurality of locations in a copying apparatus, a printer or the like.
2. Description of the Prior Art
In a copying apparatus, for example, it is necessary to assuredly catch the brightness or light emitting states of a plurality of locations. To this end, the copying apparatus is internally provided with a thermister for detecting the temperature of a fixing device, an optical sensor for detecting the amount of light emitted from a copy lamp, a reed switch for detecting the presence or absence of a copy paper sheet or for the detecting the position thereof, and the like. A plurality of signals indicative of the states of these various portions are led to a circuit board constituting a control circuit by way of a plurality of lead wires.
However, processes to be executed in the copying apparatus necessitate a high-voltage discharge and the amount of light emitted from the copy lamp is regulated by the phase control. These facts produce a certain noise at a high level and a noise signal undesirably enters a signal line such as a lead wire or the like, for example, by magnetic induction. This noise signal is sometimes erroneously detected in the conventional copying apparatus. In addition, static electricity produced outside of the apparatus body occasionally causes another erroneous detection. Accordingly, the conventional copying apparatus needs a plurality of noise filters in a circuit for detecting the state or a program for repeatedly detecting the signal within a given period of time to serve as a filter.
Otherwise, it has been considered to utilize optical fibers so that the apparatus may not be subjected to the noise caused by the magnetic induction. In this case, however, a plurality of relatively expensive photoelectric elements and a plurality of conversion circuits must be inevitably provided for respective locations to be detected, thus resulting in that the state detecting arrangement cost is undesirably high.
Furthermore, a detection level varies in compliance with the state of each location to be detected. If the states of a plurality of locations are detected in a relatively wide range in detection level and when it is necessary to assuredly catch even a fine change, the detecting circuit becomes complicated or is lowered in its performance.